drivers/scsi/scsicam.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc.
   4  *
   5  * Copyright 1993, 1994 Drew Eckhardt
   6  *      Visionary Computing
   7  *      (Unix and Linux consulting and custom programming)
   8  *      drew@Colorado.EDU
   9  *      +1 (303) 786-7975
  10  *
  11  * For more information, please consult the SCSI-CAM draft.
  12  */
  13
  14 #include <linux/module.h>
  15 #include <linux/slab.h>
  16 #include <linux/fs.h>
  17 #include <linux/kernel.h>
  18 #include <linux/blkdev.h>
  19 #include <linux/pagemap.h>
  20 #include <linux/msdos_partition.h>
  21 #include <linux/unaligned.h>
  22
  23 #include <scsi/scsicam.h>
  24
  25 /**
  26  * scsi_bios_ptable - Read PC partition table out of first sector of device.
  27  * @dev: from this device
  28  *
  29  * Description: Reads the first sector from the device and returns %0x42 bytes
  30  *              starting at offset %0x1be.
  31  * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error.
  32  */
  33 unsigned char *scsi_bios_ptable(struct block_device *dev)
  34 {
  35         struct address_space *mapping = bdev_whole(dev)->bd_mapping;
  36         unsigned char *res = NULL;
  37         struct folio *folio;
  38
  39         folio = read_mapping_folio(mapping, 0, NULL);
  40         if (IS_ERR(folio))
  41                 return NULL;
  42
  43         res = kmemdup(folio_address(folio) + 0x1be, 66, GFP_KERNEL);
  44         folio_put(folio);
  45         return res;
  46 }
  47 EXPORT_SYMBOL(scsi_bios_ptable);
  48
  49 /**
  50  * scsi_partsize - Parse cylinders/heads/sectors from PC partition table
  51  * @bdev: block device to parse
  52  * @capacity: size of the disk in sectors
  53  * @geom: output in form of [hds, cylinders, sectors]
  54  *
  55  * Determine the BIOS mapping/geometry used to create the partition
  56  * table, storing the results in @geom.
  57  *
  58  * Returns: %false on failure, %true on success.
  59  */
  60 bool scsi_partsize(struct block_device *bdev, sector_t capacity, int geom[3])
  61 {
  62         int cyl, ext_cyl, end_head, end_cyl, end_sector;
  63         unsigned int logical_end, physical_end, ext_physical_end;
  64         struct msdos_partition *p, *largest = NULL;
  65         void *buf;
  66         int ret = false;
  67
  68         buf = scsi_bios_ptable(bdev);
  69         if (!buf)
  70                 return false;
  71
  72         if (*(unsigned short *) (buf + 64) == 0xAA55) {
  73                 int largest_cyl = -1, i;
  74
  75                 for (i = 0, p = buf; i < 4; i++, p++) {
  76                         if (!p->sys_ind)
  77                                 continue;
  78 #ifdef DEBUG
  79                         printk("scsicam_bios_param : partition %d has system \n",
  80                                i);
  81 #endif
  82                         cyl = p->cyl + ((p->sector & 0xc0) << 2);
  83                         if (cyl > largest_cyl) {
  84                                 largest_cyl = cyl;
  85                                 largest = p;
  86                         }
  87                 }
  88         }
  89         if (largest) {
  90                 end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);
  91                 end_head = largest->end_head;
  92                 end_sector = largest->end_sector & 0x3f;
  93
  94                 if (end_head + 1 == 0 || end_sector == 0)
  95                         goto out_free_buf;
  96
  97 #ifdef DEBUG
  98                 printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
  99                        end_head, end_cyl, end_sector);
 100 #endif
 101
 102                 physical_end = end_cyl * (end_head + 1) * end_sector +
 103                     end_head * end_sector + end_sector;
 104
 105                 /* This is the actual _sector_ number at the end */
 106                 logical_end = get_unaligned_le32(&largest->start_sect)
 107                     + get_unaligned_le32(&largest->nr_sects);
 108
 109                 /* This is for >1023 cylinders */
 110                 ext_cyl = (logical_end - (end_head * end_sector + end_sector))
 111                     / (end_head + 1) / end_sector;
 112                 ext_physical_end = ext_cyl * (end_head + 1) * end_sector +
 113                     end_head * end_sector + end_sector;
 114
 115 #ifdef DEBUG
 116                 printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n"
 117                   ,logical_end, physical_end, ext_physical_end, ext_cyl);
 118 #endif
 119
 120                 if (logical_end == physical_end ||
 121                     (end_cyl == 1023 && ext_physical_end == logical_end)) {
 122                         geom[0] = end_head + 1;
 123                         geom[1] = end_sector;
 124                         geom[2] = (unsigned long)capacity /
 125                                 ((end_head + 1) * end_sector);
 126                         ret = true;
 127                         goto out_free_buf;
 128                 }
 129 #ifdef DEBUG
 130                 printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
 131                        logical_end, physical_end);
 132 #endif
 133         }
 134
 135 out_free_buf:
 136         kfree(buf);
 137         return ret;
 138 }
 139 EXPORT_SYMBOL(scsi_partsize);
 140
 141 /*
 142  * Function : static int setsize(unsigned long capacity,unsigned int *cyls,
 143  *      unsigned int *hds, unsigned int *secs);
 144  *
 145  * Purpose : to determine a near-optimal int 0x13 mapping for a
 146  *      SCSI disk in terms of lost space of size capacity, storing
 147  *      the results in *cyls, *hds, and *secs.
 148  *
 149  * Returns : -1 on failure, 0 on success.
 150  *
 151  * Extracted from
 152  *
 153  * WORKING                                                    X3T9.2
 154  * DRAFT                                                        792D
 155  * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
 156  *
 157  *                                                        Revision 6
 158  *                                                         10-MAR-94
 159  * Information technology -
 160  * SCSI-2 Common access method
 161  * transport and SCSI interface module
 162  *
 163  * ANNEX A :
 164  *
 165  * setsize() converts a read capacity value to int 13h
 166  * head-cylinder-sector requirements. It minimizes the value for
 167  * number of heads and maximizes the number of cylinders. This
 168  * will support rather large disks before the number of heads
 169  * will not fit in 4 bits (or 6 bits). This algorithm also
 170  * minimizes the number of sectors that will be unused at the end
 171  * of the disk while allowing for very large disks to be
 172  * accommodated. This algorithm does not use physical geometry.
 173  */
 174
 175 static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
 176                    unsigned int *secs)
 177 {
 178         unsigned int rv = 0;
 179         unsigned long heads, sectors, cylinders, temp;
 180
 181         cylinders = 1024L;      /* Set number of cylinders to max */
 182         sectors = 62L;          /* Maximize sectors per track */
 183
 184         temp = cylinders * sectors;     /* Compute divisor for heads */
 185         heads = capacity / temp;        /* Compute value for number of heads */
 186         if (capacity % temp) {  /* If no remainder, done! */
 187                 heads++;        /* Else, increment number of heads */
 188                 temp = cylinders * heads;       /* Compute divisor for sectors */
 189                 sectors = capacity / temp;      /* Compute value for sectors per
 190                                                    track */
 191                 if (capacity % temp) {  /* If no remainder, done! */
 192                         sectors++;      /* Else, increment number of sectors */
 193                         temp = heads * sectors;         /* Compute divisor for cylinders */
 194                         cylinders = capacity / temp;    /* Compute number of cylinders */
 195                 }
 196         }
 197         if (cylinders == 0)
 198                 rv = (unsigned) -1;     /* Give error if 0 cylinders */
 199
 200         *cyls = (unsigned int) cylinders;       /* Stuff return values */
 201         *secs = (unsigned int) sectors;
 202         *hds = (unsigned int) heads;
 203         return (rv);
 204 }
 205
 206 /**
 207  * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors.
 208  * @bdev: which device
 209  * @capacity: size of the disk in sectors
 210  * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders
 211  *
 212  * Description : determine the BIOS mapping/geometry used for a drive in a
 213  *      SCSI-CAM system, storing the results in ip as required
 214  *      by the HDIO_GETGEO ioctl().
 215  *
 216  * Returns : -1 on failure, 0 on success.
 217  */
 218 int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip)
 219 {
 220         u64 capacity64 = capacity;      /* Suppress gcc warning */
 221         int ret = 0;
 222
 223         /* try to infer mapping from partition table */
 224         if (scsi_partsize(bdev, capacity, ip))
 225                 return 0;
 226
 227         if (capacity64 < (1ULL << 32)) {
 228                 /*
 229                  * Pick some standard mapping with at most 1024 cylinders, and
 230                  * at most 62 sectors per track - this works up to 7905 MB.
 231                  */
 232                 ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,
 233                        (unsigned int *)ip + 0, (unsigned int *)ip + 1);
 234         }
 235
 236         /*
 237          * If something went wrong, then apparently we have to return a geometry
 238          * with more than 1024 cylinders.
 239          */
 240         if (ret || ip[0] > 255 || ip[1] > 63) {
 241                 if ((capacity >> 11) > 65534) {
 242                         ip[0] = 255;
 243                         ip[1] = 63;
 244                 } else {
 245                         ip[0] = 64;
 246                         ip[1] = 32;
 247                 }
 248
 249                 if (capacity > 65535*63*255)
 250                         ip[2] = 65535;
 251                 else
 252                         ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
 253         }
 254
 255         return 0;
 256 }
 257 EXPORT_SYMBOL(scsicam_bios_param);